Monoclonal antibodies (mAbs) against the human transferrin (Tf) receptor have several potential applications in the treatment of cancer. This NCDDG program has previously developed antibodies against the human Tf receptor that directly block receptor function and inhibit cell proliferation as anti-tumor agents. It is now proposed to investigate the use of anti-Tf receptor mAbs to deliver anti-cancer agents across the blood-brain barrier. Targeting of anti-Tf receptor mAbs to Tf receptors selectively expressed on brain capillary endothelial cells and the delivery of covalently-coupled drugs and growth factors to the brain by anti-Tf receptor mAbs has been demonstrated by other investigators. The lack of an in vitro cell model to study Tf receptor trafficking in brain capillary endothelial cells, however, has limited quantitative studies of this process and analysis of the molecular mechanism involved. In preliminary studies supported by this NCDDG program, an in vitro brain endothelial cell culture model has now been established. The specific aims of the current proposal are to use this in vitro cell culture model to characterize Tf receptor trafficking pathways in brain capillary endothelial cells; to define the molecular sorting signals involved; to optimize transcytosis of anti-Tf receptor mAbs across brain capillary endothelial cells; and to identify candidate anti-Tf receptor mAbs for preclinical trials of drug targeting via the Tf receptor in an in vivo model. The longterm goal is to develop more effective methods of treating brain malignancies by developing effective receptor-mediated delivery of anti-tumor agents to the brain. This goal will be achieved by employing existing molecular cell biological, biochemical and morphological techniques previously applied to analyze Tf receptor trafficking in other cell typed As a specific model for delivery of biologically-active fusion proteins across the blood brain barrier, the ability of a anti-human Tf receptor/IL-2 fusion protein, constructed as described in program II of this NCDDG to be targeted from the apical surface to the basolateral surface of brain capillary endothelial cells will be investigated. Interaction with other program leaders in this NCDDG and with NCI staff will continue to facilitate the transition of laboratory work performed in this program to the clinic.